[usb] Maintain a list of all USB buses

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/bus/usb.c

  *
  */
 
+/** List of USB buses */
+struct list_head usb_buses = LIST_HEAD_INIT ( usb_buses );
+
 /******************************************************************************
  *
  * Utility functions
 	if ( ( rc = bus->host->open ( bus ) ) != 0 )
 		goto err_open;
 
+	/* Add to list of USB buses */
+	list_add_tail ( &bus->list, &usb_buses );
+
 	/* Register root hub */
 	if ( ( rc = register_usb_hub ( bus->hub ) ) != 0 )
 		goto err_register_hub;
 
 	unregister_usb_hub ( bus->hub );
  err_register_hub:
+	list_del ( &bus->list );
 	bus->host->close ( bus );
  err_open:
 	return rc;
 	/* Unregister root hub */
 	unregister_usb_hub ( bus->hub );
 
+	/* Remove from list of USB buses */
+	list_del ( &bus->list );
+
 	/* Close bus */
 	bus->host->close ( bus );
 

src/include/ipxe/usb.h

 	/** Root hub */
 	struct usb_hub *hub;
 
+	/** List of USB buses */
+	struct list_head list;
 	/** List of devices */
 	struct list_head devices;
 	/** List of hubs */
 	bus->host->poll ( bus );
 }
 
+/** Iterate over all USB buses */
+#define for_each_usb_bus( bus ) \
+	list_for_each_entry ( (bus), &usb_buses, list )
+
 /**
  * Complete transfer (without error)
  *
 			     NULL, 0 );
 }
 
+extern struct list_head usb_buses;
+
 extern struct usb_interface_descriptor *
 usb_interface_descriptor ( struct usb_configuration_descriptor *config,
 			   unsigned int interface, unsigned int alternate );